The purpose of the proposed project is to evaluate a model of cortical motor control through a series of neurophysiological experiments. The model tested has been developed based on a diverse set of physiological, anatomical, and psychophysical data, with particular focus on data about cell responses in cortical areas 4 and 5 during voluntary and passive movements. Because the model proposes specific functional roles to different neural regions, it makes specific predictions regarding cell responses in these regions during novel experimental paradigms. The particular hypotheses to be tested are the proposals that tonic activities in area 4 correspond to a descending command that combines both position and force information, and that tonic activities in anterior area 5 correspond to a representation of current limb position. These hypotheses make predictions regarding the difference in cell responses between areas 4 and 5 during tasks which dissociate force-and-position information from pure position information. Two experimental paradigms are proposed to test this, one involving a comparison between isometric movements and movements with a pendulum, the other involving movements in the presence of obstacles. Aside from its relevance to the model being tested, the data obtained is expected to contribute to the understanding of cortical function during voluntary movement.